Upside Down
by Amaryllis Namikaze
Summary: It was a normal day in Moby Dick – until a small girl fell on the deck. Imagine the surprise when everyone discovers that said girl is Ace's little sister, who isn't exactly… er… normal. It's a family thing. – Fem!Luffy /DifferentDevilFruit!Luffy
1. A Small Girl and Two Fluffly Ears

**For those who will complain later, **I DID warn: Luffy is a GIRL, Luffy has a DIFFERENT Akuma no Mi and whichever comes in this story will be explained. Any questions, just _review_ (yeah, I like to bribe people).

Disclaimer: I don't own One Piece, though I wish I did. *sniff*

* * *

**Upside Down**

By _Amaryllis Namikaze_

* * *

**Prologue - A Small Girl and Two Fluffy Ears**

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_"I wanna turn the whole thing upside down_

_I'll find the things they say just can't be found_

_I'll share this love I find with everyone_

_We'll sing and dance to mother nature's songs_

_I don't want this feeling to go away."_

(Upside Down, Jack Johnson)

* * *

**I**t was a very normal day on Moby Dick - until Marco found a little girl on the deck.

She was small, maybe twelve or thirteen years old. Her black hair fell around her like a halo, but Marco figured that it probably reached her waist. She was wearing a short-sleeved red button shirt, blue jeans shorts and beige slippers. A straw hat with a red sash around it laid by her side.

"Hey, Thatch," Marco called the 4th Division Commander, who was nearby. "Do you know her?"

By now, a lot of crew members were observing the scene with curiosity. A kid wasn't frequently seen in the Moby Dick. One of their younger members was Ace, who was 21-year-old (though his maturity was questionable, according to Marco).

"Never saw such a cutie in my whole life," Thatch answered.

"Holy shit, Thatch, she's a kid, keep your _claws _to yourself," Marco smirked and some crew members laughed.

Thatch fumed, "I didn't mean it like that and ya know it, ya prick!"

"What's the ruckus?" Portgas D. Ace had arrived. He looked amused at his best friends before observing the cause of the tumult. His eyes widened. "LU?"

Marco and Thatch stopped – well, Thatch stopped shouting; Marco had remained amused and quiet. Vista came closer, "You know her, Ace?"

Ace kneeled next to the small girl, checking for injuries and likes. When he spoke again, his eyes were still surprised. "Yeah," Ace admitted. "She is my little sister."

Said little girl started to wake up after murmurs broke around. She blinked, feeling dizzy. Her eyes had an incredible hazel color. Her jaw went down after seeing Ace.

"Ace? What are you doing here?"

Ace sweat-dropped as the Whitebeard crew around them chuckled. "_You'_re the one who isn't where you're supposed to!"

"Ehhh?" 'Lu' looked around, noticing the people and the different ship. "Weird."

"Stupid Luffy," Ace reprimanded, poking her forehead.

The now identified Luffy rubbed her forehead and glared at her 'brother', though one could tell she wasn't really angry, "Bad Ace, why would you do that?"

"Because you're being silly. Now, why did you end in Moby Dick?"

"Moby Dick?" Luffy blinked owlishly.

"This ship," Ace sighed.

"Oh. I don't know."

"What do you mean _you don't know_?"

"Well, it was so fast. I was in my ship when pirates came and…-"

However, Thatch interrupted her, "Wait, wait, midget. You said _your _ship?" Some members of the crew also looked confused.

Luffy titled her head sideways, looking like a cute puppy, "Yeah, I'm a pirate Captain."

"You're what, twelve, thirteen?"

Luffy crossed her arms, pouting, "I'm seventeen, you meanie."

"EHHH?" was the sound that everybody, except Ace, made.

And, as if the situation wasn't weird enough, two fluffy black ears and a black, white-tipped tail appeared on top of Luffy's head and under her shirt. Said ears twitched and hazel eyes observed with curiosity as the Whitebeard crew around her fell back in surprise.

"So," Luffy commented to her brother, not bothered by their reactions, "is there meat here?"


	2. Kitsune Kitsune no Mi

Disclaimer: I don't own One Piece. Oda-sama does (lucky one!).

* * *

**Upside Down**

By _Amaryllis Namikaze_

* * *

**Chapter 2 – Kitsune Kitsune no Mi**

* * *

Thatch's right eye couldn't stop twitching. In the last few minutes he had been watching Ace – _Ace, of all people! – _taking care of a kid. Thatch felt like he just saw a miracle or something like that. Not that Ace was a heartless guy, it's just… well, he was an immature brat for all that Thatch knows, but here was him taking care of his little sister.

Thatch's right eye couldn't stop twitching.

"Ace-nii, your friend is funny," Luffy smiled, pointing at Thatch.

Ace rolled his eyes, bringing her small finger down, "It's rude to point, Lu."

"It's rude to walk around half-naked and you do it anyway," Luffy pointed out.

While Ace resembled a beetroot, Marco, Vista and Haruta were laughing his ass off. Thatch's right eye couldn't stop twitching.

"Ne, Ace-nii, should I run around half-naked too?"

"LUFFY!"

Luffy giggled. She looked up when she felt a hand ruffling her hair.

"You're pretty funny, kid, pretty funny," Marco told her, grinning.

She pouted, "I'm not a kid. I told you all, I'm seventeen."

"A brat, then," Marco decided.

"Not."

"Yes – your brother is twenty-one and he's still a brat to us."

Luffy made a thinking face. Ace was fuming beside her. The rest was still laughing.

"Okay, then."

"At least, you're a more likeable brat," Haruta said. Ace punched him in the head.

Luffy's ears twitched and she sniffed the air, "Is there meat here?"

"Do you eat like your brother does?" Vista decided to ask first. Luffy nodded. "Then, no, there isn't."

"Asshole," it was Vista's turn to be punched. Ace smiled at Luffy. "Of course there's meat for you, Lu. C'mon."

The small girl – well, young lady, well, whatever – stood up and followed her brother. For someone who just fell on the deck, one would say that Luffy was pretty fine.

* * *

It was only later at dinner that the commanders discovered _what _Luffy was. The dinner _table _usually was full of people talking and laughing, but, this time, it was silent, since everyone was curious about Ace's little sister (they still had trouble believing that Ace wasn't _the one _to cause trouble).

"So, tell me, midget, why do you have a tail and ears?" Thatch had finally recovered.

Luffy's hazel eyes showed confused, "Doesn't every human have?"

"Huh?" was Thatch's brilliant response.

"Ears – doesn't every human have ears?"

The crew laughed, but none as loud as Whitebeard himself. Said captain was observing the interaction.

"She got you, Thatch!"

"What a smart brat!"

"Hahaha!"

Luffy seemed happy as she chewed her meat. Ace was like a male, older version of her sitting by her side, since he was also devouring his piece of meat.

"He wants to know why you have fox ears and a tail, Lu."

"Oh," Luffy said, beaming. "Why didn't he say so? I ate the Kitsune Kitsune no Mi."

"Fox Fox, hm? I suspected your tail wasn't of a cat," Marco commented, eyeing the fluffly black tail. It was to, well, fluffy to be of a cat.

Said tail moved once in a while.

"Zoan type? Marco here is also one," Haruta pointed with his thumb to said person. Luffy stopped eating for a second, eyeing Marco, before going back to chewing.

"Aren't you curious, Lu?" Ace was surprised at his sister's actions. "By now you'd be jumping around the ship like you never saw an Akuma no Mi before."

Luffy shrugged, "Well, what can I say? I'm hungry." And eat she did.

"Say," Thatch was still curious, though. "Why you told us that you're seventeen when you're, er, _clearly _twelve?"

"Oh, because I don't have boobs?" Luffy bluntly asked and Thatch sweat-dropped. By now, each crew member was laughing, coughing awkwardly or staring with a raised eyebrow at Ace (_you taught your little sister pretty weird things, huh?_). "Kitsune have longer lives than most humans. After I ate my Akuma no Mi, I grew up slower."

"Cool," Thatch managed to answer, his eye twitched when he thought about her question once again. _What a shameless girl_, he was thinking. No one could blame the guy.

"Do you have any cool powers?" Vista asked, eyeing her small frame. It was difficult to think of this tiny girl as a Captain, much less a fighter.

Luffy took another piece of meat from other plate, "Hm. I can breathe fire and lightning, though my tail does that too. I supposedly can fly and became invisible, but still didn't manage to do that. I can enter people's dream and am training to create illusions, though I can't do it in battlefield yet. Do sneakiness and speed count as power?" She tilted her head sideways, seeing all people's, except Ace, Marco and Whitebeard, jaws on the ground. She hadn't noticed the effect that her powers had in people.

"You do all that, huh?"

"Yeah. When I ate the Kitsune Kitsune no Mi I thought I could just become a fox. Later on, Ace-nii made me search about kitsunes' legends and stuff. It's all in the books," she made a face, as if _being in the books_ should be a blasphemy.

"You said you can breathe _fire_?" Vista was thinking about the possibilities.

"Uh-hum," Luffy nodded, her bangs going up and down. Ace snorted beside her.

"And lightning too?"

"Yep."

"YOUR DEVIL FRUIT IS AWESOME!" Vista and Thatch decided after looking at each other.

Luffy didn't even bat an eyelash, "I know."

"Don't be cocky," Ace poked her forehead. Luffy didn't stop eating, but rubbed her abused forehead.

"Says the one who runs around half-naked… at least, it's your upper body and not the lower."

Ace choked on his food while Whitebeard and other crew members laughed.

"GUARARARARA!"

"What was that?" Ace poked her forehead again and again.

"Devil Ace," Luffy accused. Marco and Thatch narrowed their eyes, but if Ace was mad by this accusation, he didn't show it. He just shrugged as if he could care less and went back to eating.

These siblings were one of the weirdest things the crew had ever seen.

"The real question is: how did you manage to fall on our deck?" Marco questioned.

Luffy smiled, looking cute, but silly. "I don't know."

"Eh?"

"I had just saved Nami from Arlong when…-" Ace choked.

"You fought with someone and _won_?"

Luffy pouted, "Meanie."

"It's true."

"Is not."

"Is."

"Is not."

"Shut up, brats!" Haruta said oh-so-politely. The rest watched it as a tennis match.

Luffy stopped telling her story and Marco questioned her about.

"I was said to shut up."

Marco rolled his eyes, good-heartedly and told her that she could ignore Haruta ("Hey!").

"So, I had just saved Nami, my navigator, from Arlong when pirates attacked our ship and catapulted me through the sky. It was fun," Luffy smiled.

"You're crewmates probably are worried," Marco pointed out.

"Nah," Luffy waved in disregard. "Zoro is sleeping, Nami is bossing around, Ussop is hiding from Nami behind Zoro, and Sanji is dancing like funny spaghetti."

Whitebeard chuckled, "Won't they search for you?"

"How were you catapulted so far?" Marco wondered.

"Who are Zoro, Sanji and Ussop?" Ace asked (insert full protective-mode here).

"I suppose they will. I don't have the slightness idea. My first mate and swordsman, my cook, my sharpshooter," Luffy answered them all. She yawned, "Say, is there more meat?"

Then, all crew members looked down and noticed that – with the exception of Ace's and Whitebeard's plates – their meal had disappeared.

"GUARARARA!" Whitebeard could only laugh.

"Yep, sneakiness is a power," Ace told her little sister.

She looked up at him with big eyes, while crew members freaked out at the background ("Holy shit, how did she do that?", "I didn't even saw her hand!"), "I couldn't steal from you and Giant-san."

Whitebeard laughed as he heard his nickname. Ace patted her head in comfort, "You're not in _that _level yet, Lu."

"Meanie," Luffy told him once again. Then, she noticed the freaked out people. Luffy giggle, pointing at Thatch's right twitching eye (it had come back). "Your friend is _really _funny."

"What I told you about pointing at people? Baka!" Ace poked her forehead for the nth time. "It's rude!"

"So is running around half-naked."

"You won't let that go, will you?"

"Will you wear clothes?"

"Point taken. Let's go to the kitchen, there is more meat there."

"Yay!"


	3. Ace and Luffy

Disclaimer: I don't own One Piece. Oda-sama does.

* * *

**Upside Down**

By _Amaryllis Namikaze_

* * *

**Chapter 3 – Ace and Luffy**

* * *

"How cute, yoi" Marco commented, eyeing the scene in front of him. Ace briefly looked up from his spot on the bed and murmured a "Shut up".

Said commander was lying on his bed – each commander had their own room, after all – with his left hand supporting his hand while he observed the small girl next to him. Luffy was truly adorable, Marco supposed, seeing the black-haired kid peacefully sleeping, her head against her brother's chest and under his chin.

"Say, isn't it strange to you having your sister so young when she really isn't, yoi?" Marco was curious about since yesterday, when the said girl was catapulted to their deck. She was also a Mythical Zoan user as him, which was rare.

Ace wiggled his head, thoughtful. "When I met Lu, she had already ate her Akuma no Mi, so the situation wasn't so weird. I mean, it's strange seeing her again and noticing that she hadn't changed at all, but Lu is just special like that."

Marco narrowed his eyes, smirking. Ace's dark eyes observed his sister with a kind of love that the 1st Commander couldn't measure. It was obvious that, for Ace, this small girl on his bed meant the world to him and he would do anything to make her happy. Their brother/sister relationship was so strong that any idiot could notice it.

"But, tell me, she grows up, doesn't she?"

"Yeah."

"So, how old was she when you met her?"

Ace didn't hesitate, "Seven. She's seventeen now."

Marco quickly calculated, "So, she grows up a year physically after each two years, right? Since she looks like twelve and everything."

Ace just nodded.

"Is she strong?" Marco knew that Luffy needed to be strong, since she was a Captain and fought against Arlong, a fishman, and won. But it still was hard to believe it when he looked at her small stature and cute face.

Ace snorted, "Lu likes to think she is. I won't disagree: she's probably the strongest pirate in East Blue, but that doesn't mean anything in Grand Line, since our home is the weakest of all oceans. She needs to become stronger." His dark eyes narrowed and his expression became different.

Marco observed his reaction.

"If she is stubborn as you said, there's no need to worry about her. The stubborn ones usually survive here, yoi."

Ace sighed, absentmindedly caressing his sister's head. She smiled in her sleep and cuddled closer. It was a really cute sight.

"It's the usually that worry me."

Marco smirked once again, "I sense a brother complex."

"What? No way?"

"Of course you're over-protective of her…"

"I'm not!" Ace _stubbornly _shouted. Then his eyes widened and he looked down. Thankfully, Luffy was still sleeping. "I'm not," he repeated, this time whispering.

"I mean, who wouldn't be?" At Ace's questioning glance, Marco explained, "She's tiny and, for what I saw until now, really naïve. She's heading toward Grand Line with a small crew. And, even though she's seventeen, her appearance is _really _younger. I can't blame you for being worried, yoi – I know that if I was her older brother, I would."

Ace looked at his best friend for a few moments before speaking. "You know, Marco, if something happen to me," Here the blond narrowed his eyes, "I'll trust you to take care of her. So, in a sense, yeah, you're her older brother too."

Marco stayed in silence for a few minutes, realizing the huge confidence his friend was depositing in him. He knew that anything could happen in those oceans and, though he would try to prevent it, _anything _could happen to Ace. Taking care of his little sister was something he wouldn't trust to anyone – so, Marco nodded positively.

"Of course," he said, heading back for the door. "Ah, I came here to alert you that breakfast is ready and you know how much everybody eats, if you want some, come now, yoi."

"Thanks, Marco," Ace thanked, but both of them knew that he wasn't referring to the breakfast alert.

Luffy mumbled something incomprehensible and sighed in happiness. Ace continued caressing her head.

* * *

Later that day, Marco, Luffy, Ace, Thatch and other crew members leisured on the deck, finally resting from their day. Luffy hadn't done pretty much anything, just followed Ace around like a puppy while said commander did his duties – it was a cute scene, making the crew who saw it smile. They were used to thinking about the fire-user being their brat and younger brother, so, seeing _he _being the responsible one was kind of new.

"Ne, Ace-nii, when did you ate an Akuma no Mi?" Luffy asked suddenly.

"Before meeting Pops, that I can say," Ace answered, ignoring Marco's and Thatch's snorts.

"Why do you call Giant-san 'Pops'?"

"Because he calls us sons," Ace patiently responded.

"Why did you enter his crew?"

"Aren't you a curious one?" Vista questioned before Ace could say anything.

Luffy titled her head sideways, "Why would you say that?" She didn't understand when the people around her started to laugh, so, she laughed too. What was so funny, anyway?

Ace sat up and Luffy mimicked him. "Tell me about your adventures until now, Lu. I know you; you're a probably itching to shout it."

Luffy pouted and the crew members laughed.

"Meanie."

"So you say," was Ace's answer.

"Well, there's Zoro, who is really, really, really funny."

"He tells jokes?" Thatch raised a eyebrow.

Luffy shook her head, long black hair flying everywhere. "Uh-huh. He always getting lost and napping. He _really _likes sake and is always calling Nami an annoying woman, but never hesitates to protect her."

"Have you ever considered that he's in love with her, yoi?" Marco grinned. The kid was adorable, he'd give her that.

Luffy made a thoughtful face, "Nah. Zoro doesn't like Nami, it's just that he's the most loyal person in my crew."

"How so?" Ace was curious, after all, he knew that his baby sister saw the world in a different way. A weird, but honest one.

"He never, never, neeeever doubt me. My crew thinks of me as someone easy-going and playful – Zoro is the only one who knows me more and obeys without questions."

"Shouldn't every crew member do this?" Vista asked, confused.

"Usually, yes. But I don't really care about," Luffy shrugged. "They know I'm the Captain in the right moments – that's enough for me. I can't fight with swords, nor cook, nor navigate, nor shoot. I wouldn't be anything without my nakama, they're my family."

Everybody smiled at the girl. She was naïve, but wise in her own way.

Suddenly, a random crew member ran toward the group, "Pops asked me to alert everyone that we're stopping by an island. It looks inhabited, so we'll rest there for a few days." Everyone nodded in acknowledge.

"Ne, Ace-nii, do you think we could spar there?" This caught everybody's attention – this _little girl _against Fire Fist Ace?

"Sure, Lu. Beware, though, that I'm much stronger than before."

Luffy smiled, "So am I, baka."


	4. Stronger

Disclaimer: I don't own One Piece. Oda-sama does.

* * *

**Upside Down**

By _Amaryllis Namikaze_

* * *

**Chapter 4 - Stronger**

* * *

It was already middle afternoon when the spar eventually happened. The island, as Hotoru (the crewmember that warned them) said, was inhabited. They decided to camp in the beach, since everybody wanted to stay out of the ship and look at the stars. Whitebeard himself managed to convince his nurses (with the help of Luffy's puppy, er, foxy eyes) that it was a good idea even for him to go camping.

By now, all Whitebeard crew considered the little girl their younger sister – which was something, seeing that she was there for only one day. Being so, it was no surprise that everybody was curious to see Ace's and Luffy's spar. For obvious reasons, the bets were in Ace's favor, but it didn't mean that it discouraged Luffy.

Actually, she was really excited – she wanted to see how much stronger her brother had become.

They were facing each other in the beach. The crew watched around them, giving a _very_ huge open space, knowing Ace's techniques and expecting nothing less than _explosive _from Luffy, if she was anything like him.

"You know you'll lose," Ace commented, smirking slightly when Luffy huffed.

She crossed her arms, "I never won, even when you weren't a Devil Fruit user. My chances of winning are ridiculous and we both know it."

Ace raised an eyebrow. "Then, why did you decide to fight against me?"

"To see how much stronger you are. To see how much stronger _I am_," Luffy shrugged.

Ace clapped his hands and got ready, "Alright, when you're ready…"

Luffy wasted no time, running toward him. She was incredibly fast, some noticed, and graceful. The black-haired girl closed her hand in a fist, going for a punch. It, however and unsurprisingly, didn't affect the fire-user in the least. He stayed exactly where he was as Luffy observed her right hand – she extinguished the flames with her black, white-tipped tail, which confused everyone, since it appeared to not hurt her.

"So, you're a Logia type," Luffy noticed, her voice full of happiness. Ace's smirk still splattered on his face. "Since you are fire, it'll be difficult to counter-attack… but I might just have the power for it."

Ace stopped smirking, a frown forming on his face, "What do you mean?" _Has she learnt Haki?_ Even so, it was very unlikely.

Luffy grinned in a silly way.

"Usually, I wouldn't try to do that in a fight, since I never tested it before, but seeing that it's just you and me…" And, saying this, Luffy brought her hands together, as if praying, "Kitsune Kitsune no Hybrid Transform!"

Her ears emerged atop of her head once again; black, white-tipped fur forcing the straw hat to fall against her back. The solitary tail gave place to another one, equally black, fluffy and white-tipped – both of them moved now and then. Her hazel eyes turned bigger and reddish-yellow with vertical pupils. Normal fingernails became longer and sharper. All in all, she looked like a human-fox creature.

Ace, of course, was used to such transformation, but the other people there weren't – gasps of surprise were heard through the crowd of crewmembers. Marco found himself observing the details of it, since he never met another Mythical Zoan user.

Luffy's tails curled around her waist and she covered their white tips with her hands, "Kitsune-bi (Fox Fire)!" Fire, _real fire_, came out of the tails, its bluish-white color dancing.

Ace observed, "What of it, Lu? You can control fire since when we were kids." Actually, only after Sabo died, but he wasn't about to say it out loud.

Luffy nodded, still smiling, "Yep. But after you started your pirate life, I started to train my control over fire and lightning, since that before I could just throw fireballs and such."

"And now you…?"

"Now, I can control the _real _fire of kitsune. I made some research about it-"

"You read about without someone ordering you to do it? I'm impressed," Ace laughed. Luffy's smile grew wider.

She laughed too.

"Anyway. I discovered that Kitsune-bi is a little different from common fire, as I can touch fire with my tails and don't get hurt. So, if I'm correct…" But Luffy didn't need to finish her phrase, because Ace did it.

"If you're correct, you can touch me."

Luffy nodded - this wide smile still on her face, "Shishishishi."

Ace wiggled his head in a thoughtful manner.

"I gotta admit: you really got stronger." With that, he became ready – this time, for serious.

The black-haired girl left her tails fall by her side, both of them still full of bluish-white flames. She ran forward and aimed for a punch only that it was with her right tail instead of her fist. Ace dodged, immediately trying to kick Luffy behind her knees, but she jumped and punched him with both tails. Ace flew across the sand – two bruises forming on his chest.

"Being a Logia type, you probably became used to not being hit. When was the last time, nii-chan?" Ace's answer was a fire fist punch. This time who flew across the beach was Luffy, though she quickly extinguished the fire on her belly with both tails – the blue fox fire apparently had no effect on her body.

Punch and kicks went everywhere while the two siblings dance around each other. For Ace, it was obvious that his sister had gotten better. For Luffy, it was obvious that her brother was worthy his title of "Fire Fist Ace" and "2nd Commander". Fists full of flames and tails full of fox fire fought. However, Luffy had a weaker body and was slower, tiring faster than her older brother. So, she jumped back, creating a few meters of distance between Ace and her.

She was panting, Luffy noticed, but so was Ace. Good – in the past, making Ace pant was impossible.

"That's… all?" Ace managed to say between gasps for air. He was clutching his ribs, where Luffy had "tail'ed" him.

Luffy surprised everyone, except Whitebeard and Ace, when she smiled widely and happily, "Onii-chan got stronger. There still is so much difference between us that it's almost unfair," she said, panting. "But I'm happy, because I got stronger too."

"Sou ka," Ace commented, returning the smile. His eyes widened when Luffy sighed one last time and fell back. "Luffia?" He ran toward her, only to laugh in relief when he realized she was just sleeping.

"It was a good fight, son," Whitebeard told him, patting his back when Ace stood up with Luffy in his arms.

"Thanks, Pops."

"I wouldn't expect someone so small to be so determined," Marco confided him when Ace reached his sleeping bag.

Ace chuckled, carefully depositing Luffy on his sleeping bag.

"That's just her. Well, I can't say anything really… I didn't expect her to be so stronger… I guess I was used to frail, whining little Lu."

Marco smirked at his friend's eyes, "I said you have a brother complex, yoi."

"I do not!"

"Ha! I can imagine when she introduces her boyfriend to you."

"She _won't_ introduce because she _won't _have a boyfriend."

"Brother complex, yoi, brother complex."

"Urgh, shitty phoenix."

Luffy rolled over the sleeping bag, making herself more comfortable, "Hm, meat," she mumbled and rolled over again. Marco and Ace laughed quietly.

* * *

**Onii-chan – **older brother

**Sou ka – **"I see", "Is that so?" or just "Oh?"

**Kitsune-bi – **fox fire

* * *

Thanks for the reviews, people! I wasn't sure if you'd like my plot, because I never wrote about One Piece. So, thanks to your reviews, I'm more confident to try it.

Until next time!

Amy.


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